Gas turbine engines, which are often used to propel aircraft, typically comprise a core engine which is surrounded by a nacelle. A bypass air duct is formed between the core engine and the nacelle. Air which enters the gas turbine engine is driven by a fan assembly along the bypass duct and provides a forward thrust at the rear of the engine.
In certain situations, such as during landing, it is necessary to slow the speed of the aircraft down significantly. Whilst this can partially be achieved using air brakes which are often present on the wings of an aircraft, it is also necessary to provide a reverse thrust from the gas turbine engines in order to further reduce the speed of the aircraft. In order to divert some of the air which passes through the engine to provide a reverse thrust, a thrust reverser may be arranged in the nacelle surrounding the fan assembly. Electric thrust reverser actuation systems may operate using a clamshell (see e.g. U.S. Pat. No. 5,826,823), blocker door (see e.g. U.S. Pat. No. 9,181,898) or translating cowl arrangement.
In a translating cowl arrangement, for example as seen in U.S. Pat. No. 8,904,751, the thrust reverser typically comprises a translating cowl mounted to the nacelle, a cascade within the nacelle, and blocker doors. When reverse thrust is required the translating cowl is translated so as to expose the cascade and the blocker doors are moved into the bypass duct so as to direct airflow through the cascade and out of the nacelle. The cascade typically comprises vanes which direct the airflow against the direction of the air which enters the engine and this provides a reverse thrust.
In typical thrust reverser architectures the cascade is arranged in a fixed position in the nacelle. The translating cowl is often mechanically linked to the blocker doors such that when the translating cowl slides opens it pivots the blocker doors relative to the cascade and radially inward into the bypass duct, resulting in bypassed air within the duct being diverted from the duct through the cascade.
The applicant has realised that at least some thrust reverser designs can introduce efficiency losses in the turbine engine, especially during the production of forward thrust. When the blocker doors are moved by the motion of a translating cowl, even in a stowed position the blocker doors may partially protrude into the bypass air flow path and causes efficiency losses. The applicant is aware of a thrust reverser comprising a translating cowl and a separate translating cascade linked to the blocker doors, with the blocker doors stowed away and fully hidden from the bypass air flow path so that the bypass ducting becomes more streamlined with less drag losses in flight, thus reducing the efficiency losses of the engine.
The applicant has now recognised that it may be undesirable to provide separate drives for each of the components in such a thrust reverser to move them into position, i.e. for moving the translating cowl and the cascade separately.
The present disclosure seeks to provide an improved actuator for a thrust reverser, and a thrust reverser comprising such an actuator.